1. Field
The invention relates to a modified diene elastomer comprising predominantly the diene elastomer functionalized in the middle of the chain by an alkoxysilane group, optionally hydrolysed, bearing a tertiary amine functional group and functionalized at the chain end by an amine group. The invention also relates to a process for the preparation of such a modified diene elastomer, to a composition comprising it, and to a semi-finished article and a tire comprising this composition.
2. Description of Related Art
Now that savings in fuel and the need to protect the environment have become a priority, it is desirable to produce mixtures having good mechanical properties, in particular good stiffness and a hysteresis which is as low as possible in order to be able to process them in the form of rubber compositions which can be used in the manufacture of various semi-finished products participating in the composition of tire casings, such as, for example, underlayers, sidewalls or treads, and in order to obtain tires having a reduced rolling resistance.
The reduction in the hysteresis of the mixtures is an ongoing objective which has, however, to be done while retaining the suitability for processing, in particular in the raw state, of the mixtures.
Many solutions have already been experimented with in order to achieve the objective of fall in hysteresis. Mention may in particular be made of the modification of the structure of diene polymers and copolymers for the purpose of polymerization by means of functionalization agents or else the use of functional initiators, the aim being to obtain a good interaction between the polymer, thus modified, and the filler, whether carbon black or a reinforcing inorganic filler.
Mention may be made, by way of illustration of this prior art, of the use of diene elastomers functionalized by alkoxysilane compounds bearing an amine functional group.
Mention may be made of Patent FR 2 867 477 A1, which claims the functionalization at the chain end with compounds of (dialkylaminoalkyl)trialkoxysilane, and also a rubber composition based on silica or carbon black. Mention may also be made of U.S. Pat. No. 8,071,689 B2 and U.S. Pat. No. 8,106,130 B2, which respectively claim, for one, the functionalization at the chain end with the trialkoxysilane compound bearing a nitrogen-based group, the nitrogen atom being included in a substituted or unsubstituted aromatic heterocycle, and, for the other, with an alkoxysilane bearing an amine functional group having at least one alkoxysilyl group and at least two tertiary amine groups. Finally, mention may be made of Patent Application WO2009133068A1, which indicates that the functionalization in the middle of the chain with an alkoxysilane compound bearing a secondary or tertiary amine functional group makes it possible to improve the raw processing/hysteresis compromise in comparison with a functionalization at the chain end.
Provision is made, in Patent JP4655706B2, to combine the functionalization of the living chain end with a compound of the alkoxysilane type bearing an amine functional group with the initiating with an amine-functional alkyllithium with the aim of minimizing the hysteresis. In the same way, provision is made, in Patent Application US20120245275A1, to combine the functionalization of the living chain end with a compound of the alkoxysilane type bearing an amine functional group with the initiating with a lithium amide but also with the copolymerization with a functional monomer of the vinylaminosilane type.
These functionalized elastomers have been described in the prior art as effective in reducing hysteresis. Nevertheless, it turns out that the compositions comprising elastomers thus modified do not always exhibit a satisfactory hysteresis, an acceptable processing and mechanical properties satisfactory for use as tire tread.
For this reason, research studies have been carried out on other functionalization reactions for the purpose of obtaining rubber compositions having an improved raw processing/hysteresis/stiffness compromise.